Semitrailer dolly and tracking trailer for freight containers

ABSTRACT

A dolly is provided for supporting and connecting a semitrailer to a towing vehicle and particularly to a preceding semitrailer or trailer to form a train of trailers. Each dolly comprises crossed towing bars for effecting absolute tracking of a semitrailer and fifth wheel means for engaging a semitrailer. A tracking trailer for freight containers is also provided, the tracking trailer having crossed towing bars for connection to a towing vehicle. The invention also resides in the provision of towing bars for the tracking trailer and dolly of a size and weight which permits for manual handling thereof. In addition, guide plates are provided which are substantially triangular in cross section and are adapted to align and position containers on a semitrailer or trailer.

United States Patent [72] Inventors James Veenema 245 Arbor Road,Franklin Lakes, 07417; Fred Muller, Jr., 120 Ridgedale Ave., FlorhamPark, 07932; John A. Johnson, Sl xq'idgnDrive. Short Hills. N..I. 07078[21] Appl. No. 779,708 [22] Filed Nov. 29, 1968 [45] Patented Apr. 20,1971 [54] SEMITRAILER DOLLY AND TRACKING TRAILER FOR FREIGHT CONTAINERS11 Claims, 12 Drawing Figs.

[52] U.S. Cl 280/408, 280/418, 280/442, 296/35 [51] Int. Cl 862d 53/00[50] Field of Search 280/408, 418, 442; 296/35, 35 (.1); 105/366 (.8)

[56] References Cited UNITED STATES PATENTS 642,394 l/l900 Watkins280/442X 1,892,004 12/1932 Reid 280/418 2,124,947 7/1938 Henderson280/442 Primary Examiner- Leo Friaglia Attorney-Lawrence l. LernerABSTRACT: A dolly is provided for supporting and connecting asemitrailer to a towing vehicle and particularly to a precedingsemitrailer or trailer to form a train of trailers. Each dolly comprisescrossed towing bars for effecting absolute tracking of a semitrailer andfifth wheel means for engaging a semitrailer. A tracking trailer forfreight containers is also provided, the tracking trailer having crossedtowing bars for connection to a towing vehicle. The invention alsoresides in the provision of towing bars for the tracking trailer anddolly of a size and weight which permits for manual handling thereof. Inaddition, guide plates are provided which are substantially triangularin cross section and are adapted to align and position containers on asemitrailer or trailer.

Patentecl 4 April 20, 1971 3,575,444

4 Sheets-Sheet 1 INVUN'IURS' JAMES VEENEMA FRED MULLER,JR BY I JOHNALGOT JOHNSON 5 ATTO NEY Patented A ril 20, 1971 3,575,444

4 Sheets-Sheet 2 v lNVliN'I'U/(S' JA VEENEMA FR MULLER,JR. y JOHN ALGOTJOHNSON A ORNEY Patented April 20, 1971 4' Sheets-Sheet 5 w w H NAM Y 1M0 E W N Nm R .IELO. T vi Q/ T M A s EDN i Patentd "A ril 20, 1971 I3,575,444

4 Sheets-Sheet 4 lNVliN'l'U/(Sf JAMES VEENEMA FRED MULLER, JR. BY JOHNALGOT JOHNSON ATTORNEY SEMITRAILER DOLLY AND TRACKING TRAILER FORFREIGHT CONTAINERS BACKGROUND OF THE INVENTION This invention was madein connection with the development of a semitrailer or trailer forfreight containers which could be used in a train of trailers and/orsemitrailers for transporting containers from a point of arrival tostorage area. In the past, it was common to load a trailer orsemitrailer and then, if the goods were to be shipped by sea, rail,airplane, barge or other form of transportation before reaching theirfinal destination, unload the trailer or semitrailer when reaching thepoint of departure of the further transporting means for loading ontothe further transporting means.

Great savings in time and expense have been effected by the use ofdoor-to-door" containerization which has been achieved by using trailersor semitrailers which mount independent containers. The independentcontainers can be removed from the trailer or semitrailer as a unit andmounted on or in the next means of transportation. For example, it iscommon to load a ship by using cranes which pick containers off trailersand/or semitrailers and position them in the hold of the ship. Unloadingis effected by removing the containers from the hold and placing them onthe dock or waiting trailers and/or semitrailers. Preferably, thecontainers are loaded on trailers or semitrailers directly.

It has been found that ships can be loaded and unloaded more rapidlythan the trailers or semitrailers can be moved into loading positions.Further, a separate cab or tractor and its driver has been required foreach trailer or semitrailer. It has been proposed that a single tractorbe used to pull a plurality of trailers and/or semitrailers to savecosts, time and space.

It is already known that two or more trailers can be pulled by a singletractor. Such double-bottom" transportation is presently only permittedon expressways which are relatively straight. The double-bottom conceptwould not be feasible in a docking or loading and storage area due tothe fact that turning of a train of two or more trailers and/orsemitrailers in tandem requires a very large area. For example, when atractor with four trailers turns a corner, the tractor uses a certainarea defined by a certain radius or arc. The trailer directly connectedto the tractor turns in a somewhat larger arc. The nextsucceeding'tailer turns in yet a larger arc, and this phenomenoncontinues until the last trailer needs a very large corner indeed. Thus,since the towed vehicles do not track, the double-bottom method wasdeemed not to be feasible for thepresent purposes.

SUMMARY The term trailer is used herein to describe a vehicle capable ofbeing towed which is fully mounted on wheels so that it need not also besupported while being towed. The term semitrailer"is used to describe avehicle which has wheels mounting the rear portion and, in order to betowed, requires that the front portion be supported. The expressionfifth wheel means" is used herein in the sense well known'in the art todescribe the means by which a tractor is connected to a semitrailer.

This inventionresides in the provision of a tracking trailer for freightcontainers and a dolly for a semitrailer each of which has crossedtowing bars for causing the trailer or semitrailer to track behind atowing vehicle. The towing bars are of a weight which permits manualhandling thereof and may be connected directly to a tractor or to apreceding trailer or semitrailer. The dolly is provided with fifth wheelmeans for engaging a semitrailer.

The use of crossed towing bars for effecting tracking of a towed vehicleis known; see, "for example, US. Pat. Nos. 1,990,484; 2,124,947; and2,313,235. Nevertheless, the problem of providing a train of trailersand/or semitrailers which could be towed by a single tractor and bemaneuvered in a small area has remained unsolved. Perhaps the principalreason that this problem has remained unsolved is that those skilled inthe art, if they even contemplated the use of towing bars, assumed thatthey would not be feasible as will be explained more fully.

Seinitrailers and trailers which are used for the shipment of freight byindependent freight containers are usually 20 to 40 feet long and carryloads often in excess of 50,000 pounds. A train of five such trailerscould easily weigh in excess of 375,000 pounds. Thus, if one consideredthe use of towing bars for connecting the trailers and/or semitrailers,one would immediately assume that such towing bars must be quite strongand therefore quite bulky and heavy. For a connecting means betweentrailers to be feasible, it must be one that can be manually handled.Towing bars which could accommodate the compressive-tensile and bendingloads assumed to be incurred would be too bulky and heavy to be manuallyhandled.

The present invention resides in the provision of towing bars fortrailers for freight containers and semitrailers which can be manuallyconnected to and disconnected from a towing vehicle. It was found thattowing bars for trailers for freight containers and semitrailers forfreight containers need not be capable of withstanding nearly as largebending forces as the tensile-compression forces that they must handlesince such trailers or semitrailers are used in areas of relativelylevel grade. Storage areas adjacent points of arrival are usually quitelevel, only slight grades being present and no hills. For example,docking areas and the areas around a railroad freight yard are usuallyquite level. With this in mind, towing bars were developed which couldresist large tensile-compression forces but which could not resist aslarge bending forces and which could be manually handled. A preferredembodiment of such towing bars is made of steel and comprises a hollowcentral portion.

The invention further resides in the provision of guide plates for thesemitrailer or trailer beds which aid in aligning and mounting differenttype containers on the beds. The guide plates are mounted for movementto an inoperative position below the bed or to an operative positionabove the bed.

When in the operative position, the guide plates present slopingsurfaces which are engaged by the freight containers and guide them intoposition. The guide plates have substantially triangular cross sections.

BRIEF DESCRIPTION OF THE DRAWING The objects and features of theinvention will become more apparent by reference to the followingdescription taken in conjunction with the accompanying drawing, inwhich:

FIG. 1 is a side elevational view of a semitrailer attached to a dollyin accordance with the invention;

FIG. 2 is a plan view of the semitrailer and dolly of FIG. 1;

FIG. 3 is a perspective view of a towing bar in accordance with theinvention;

FIG. 4 is a side elevational view of the towing bar of FIG. 3;

FIG. 5 is a plan view of the towing bar of FIG. 3;

FIG. 6 is a plan view of a tracking trailer in accordance with theinvention;

FIG. 7 is a side elevational view of the trailer of FIG. 6;

FIG. 8 is a schematic illustration of a train of tracking trailers inaccordance with the invention tracking behind a towing vehicle;

FIG. 9 is a side elevational view of a guide plate in accordance withthe invention;

FIG. 10 is a front elevational view of the guide plate of FIG.

FIG. 11 illustrates the mounting of the guide plate of FIGS.

9 and 10 on a crossmember of a tailer bed; and, s

FIG. 12 is a schematic illustration of a preferred manner of pivotallyconnecting the guide plate of FIGS. 9 and 10 to a trailer bed.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, adolly 1 in accordance with the invention is shown attached to asemitrailer 2 by fifth wheel means 3. The semitrailer comprises a flatbed 19 adapted to receive independent containers of the door-to-door"containerization type and has the usual rear wheel assembly 18 which isfixed relative to the trailer bed.

The dolly 1 comprises a chassis 4 and wheels 5 mounted on axles 6. Thechassis includes fifth wheel engagement means 7 for engaging a kingpinor pivot means projecting downwardly from the bottom of the semitrailer2. Kingpin 15 is spaced from the kingpin 15a of the semitrailer. Suchmeans are well known in the art and are not specifically illustrated ordescribed. The semitrailer 2 has a folding support 14a for supportingthe front end of the semitrailer when it is not connected to a tractoror dolly. Where the kingpin 15a is normally 2 feet 6 inches from thefront end of the semitrailer, kingpin 15 is ll feet from the front endof the semitrailer.

Pintle hooks 8 are connected to one end of the chassis at spaced-apartpoints. It will be noted from viewing FIG. I that the pintle hooks 8 aredisposed on opposite sides of the longitudinal axis of the trailer 2when the dolly is connected to the trailer. It will be noted fromviewing FIG. I that the pintle hooks are disposed at different levelswith respect to the chassis.

The dolly further comprises towing bars 9. Each towing bar has tow rings10 and 11 attached to its ends. The tow rings 10 at the inward end ofeach bar are pivotally connected to the chassis by engagement with thepintle hooks 8. As illustrated, the towing bars are crossed. Suchcrossing is accommodated by the positioning of the connections of therings 10 to the chassis at different levels of the chassis and thespacing and pivotal connection of the tow rings 10. The tow rings 11 onthe outward ends of the towing bars 9 when connected to a towing vehicleare pivotally connected thereto at levels corresponding to the levels ofconnection of the tow rings 10 to the chassis 4.

As noted previously, semitrailers with which the present dollies areintended for use are usually about 40 feet long. In the preferredembodiment of the invention, each towing bar from the center of each towring to the center of the other tow ring is 12 feet long. The distancebetween the axis of the pivotal connection of the fifth wheel engagementand the forward end 12 of the semitrailer is about I l feet. Thedistance between the axis of the fifth wheel means and the center ofthepintle hooks 8 is 3 feet. The towing bars when crossed extend beyond theend of the trailer at distance which is approximately 2 feet.

Towing bars weighing more than about 200 pounds cannot be easilymanually handled. It will be appreciated that a towing bar weighing 200pounds and connected at one end to a pintle hook requires a liftingforce of only 100 pounds at the outward end since an upward force of 100pounds will be present at the engagement of the towing bar with thepintle hook.

Reference will now be made to FIGS. 3, 4 and 5 in which a preferredembodiment ofa towing bar 9 is illustrated. It will be noted that thebody 14 of the towing bar 9 is hollow along its entire length. The ends13 of the tow rings are inserted into the ends of the towing bar.

A specific preferred embodiment of the towing bar is made of a steel ofhigh tensile-compression strength and has a total of approximately100,000 pounds tensile-compression strength. The outside diameter of thebar is 2% inches. The inside diameter is 2 5/16 inches leaving a totalradial thickness of seven-sixteenths of an inch. Though the said towingbar is over 12 feet long when including the length of its tow rings, itweighs less than 200 pounds. This has been achieved by the provision ofthe central hollow portion. The bending forces necessary to bend thesaid towing bar are much less than that which could cause damage due toexcessive tensilecompression forces. However, towing bars as describedhave been used in practice and have been found to be completelysatisfactory and to provide for absolute tracking.

The towing bars have also been found to be easily manually connected toand disconnected from a preceding towing vehicle. This is due to therelative lightweight of the towing bars which has been made possible bythe unique realization that the bending forces in an area ofsubstantially level grade would be much less than thetensile-compression forces that the towing bar is subjected to. In thisregard, the weight of a loaded semitrailer often exceeds 50,000 pounds.When four of five semitrailers are being towed loads exceeding 375,000pounds may be towed which loads can be easily accommodated by two towingbars each having a total tensilecompression strength of 100,000 pounds.

Referring now to FIGS. 6 and 7, a tracking trailer 20 for freightcontainers in accordance with the invention is shown. The trackingtrailer comprises a conventional flatbed 21 and a rear wheel assembly 22similar to the semitrailer rear wheel assembly 18. The trailer bed 21is, similar to the semitrailer bed 19, adapted to receive independentfreight containers of the door-to-door containerization type. A forwardwheel assembly 23 is rotatably connected to the trailer bed by meanswell known in the art. The rear wheel assembly is not rotatable relativeto the trailer bed.

Towing bars 24 similar to the towing bars 9 of the dolly 1 of FIGS. 1and 2 are connected to the frame 25 of the forward wheel assembly in thesame manner that the towing bars 9 are connected to the chassis 4 of thedolly. Thus, the towing bars 24 are adapted to be crossed for connectionto a towing vehicle.

Pintle hooks 26 and 27 are mounted on the rear end of the trailer 20 andare adapted for engagement by the towing bars of a dolly or trackingtrailer to be towed by the trailer 20. The semitrailer 2 shown in FIGS.1 and 2 may be provided with similar pintle hooks 16 and 17.

Referring to FIG. 8, a schematic illustration of the movement of a trainof trailers and/or semitrailers towed in the directions of the arrows30, 31 is shown. It has been found in practice and may be appreciated bya study of FIG. 8 that whether you have two or more trailers and/orsemitrailers in the train, they can turn any corner that a tractortrailer can turn. Thus, the present invention enables a train oftracking trailers and/or semitrailers to be operated and maneuvered in acontainer storage area with little or no difficulty.

Semitrailers or trailers of the type described and illustrated canaccommodate any combination of containers the total length of which is40 feet or less. Thus, four 10-foot containers can be accommodated, two20-foot containers, or one 40-foot container or any other combinationadding up to 40 feet or less. It has been found that it is necessary toprovide for at least 6 inches misalignment in any direction for a20-foot container which is to be placed on a 40-foot trailer withanother 20-foot container. For a 40-foot unit, a slightly largermisalignment may be tolerated. Though the foregoing allowances wouldseem to be quite large, it will be appreciated that an angularmisalignment of only 1 with a 40-foot container can result in lateralmisalignment of 2 inches and in a fore-and-aft" misalignment of 5inches.

Referring now to FIGS. 9-12, a guide plate 40 in accordance with theinvention is shown. The guide plate 40 has a triangular or wedge-shapedcross section as can most clearly be seen in FIG. 10. It is made ofasingle sheet of material, such as steel, and may be coated withantifriction means. The triangular or wedge-shaped cross sectionprovides sloping side walls which the containers engage when loweredtoward the trailer beds. The sloping sidewalls guide the containers totheir loaded positions. The use of the aforementioned antifriction meanswould aid in facilitating such guiding and the resultant slidingmovement of the containers.

The guide plate 40 is pivotally connected to the bed 41 of a trailer orsemitrailer by bolts 42 or similar means. In the schematic illustrationof FIG. 12 a preferred manner of mounting the guide plate is shown inwhich the guide plate is pivotally connected between transverse members43 in such a manner that it can be pivoted to a first or inoperativeposition out of the plane of the bed or to a second or operativeposition above the plane of the bed.

A specific preferred embodiment of the guide plate for use on a traileror semitrailer as described and illustrated has a total height of 12%inches and is mounted so that it extends approximately inches above thebed when in its operative position. The base portion 44 is approximately3 inches in cross section and the apex 45, where the ends of the metalforming the plate meet, is approximately three-quarters of an inch incross section. With the aforesaid guide, misalignment was held to aminimum and it was found that a container could be loaded with only acrane operator and driver without the usual spotter previously requiredto direct the crane .operator.

While the various features of the invention have been disclosed inconjunction with a specific embodiment chosen for purposes ofillustration, it is apparent that numerous changes could be made withinthe scope of the inventive concepts involved and it is, accordingly,intended that the invention not be limited except by the language of thefollowing claims.

We claim:

1. A dolly for supporting a semitrailer and connecting it to a towingvehicle for movement along substantially flat terrain, said dollycomprising chassis means including fifth wheel means for engaging asemitrailer, wheel means mounting said chassis means and including atleast one pair of wheels mounted on a common axis, a pair of towing barsof equal length each having a first end pivotally connected to one endof said chassis means and a second end having pivotal engaging means forpivotal connection to a towing vehicle, each said towing bar beingadapted to be manually connected to and disconnected from a towingvehicle, said first ends of said towing bars being pivotally connectedto said one end of said chassis means at spaced-apart points on oppositesides of a line perpendicular to said common axis at a point midwaybetween said pair of wheels, said spaced-apart points being at differentvertical levels with respect to said chassis means, and said pivotalmounting of said first ends of said towing bars at said spaced-apartpoints and said different levels being such that the towing bars areadapted to be crossed for said pivotal connection to the towing vehicleso that the semitrailer will track behind the towing vehicle.

2. A dolly as claimed in claim 1, wherein each said towing bar is hollowalong substantially its entire length.

3. A dolly as claimed in claim 2, wherein each said towing bar has atensile-compression strength of at least 100,000 pounds. I

4. A dolly as claimed in claim 1, wherein each said towing bar comprisesa central portion in the form of a hollow steel tube.

5. A dolly as claimed in claim 4, wherein the semitrailer to beconnected to a towing vehicle is approximately 40 feet long, each saidtowing bar is approximately 12 feet long, said semitrailer compriseskingpin means disposed approximately ll feet from the forward end of thesemitrailer for engagement with said fifth wheel means of said dolly,and said towing bars are connected to said dolly approximately 3 feetforward of the expected center of engagement of said kingpin means insaid fifth wheel means.

6. A tracking trailer for freight containers for movement alongsubstantially flat terrain, comprising an elongated flat bed forreceiving freight containers, wheel means movably mounting andsupporting said bed, said wheel means including at least one pair ofrear wheels mounted on a first common axis fixed relative to said bedand forward wheel means rotatably connected to said bed, said forwardwheel means including frame means and at least one pair of front wheelsmounting said frame means, said pair of front wheels being mounted on asecond common axis, a pair of towing bars of equal length each having a'first end pivotally connected to one end of said frame means and asecond end having pivotal engaging means for pivotal connection to atowing vehicle, each said towing bar being adapted to be manuallyconnected to and disconnected from a towing vehicle, said first ends ofsaid towing bars being pivotally connected to said one end of said framemeans at spaced-apart points on opposite sides of a line perpendicularto said second common axis at a point midway between said pair of frontwheels, said spaced-apart points being at different vertical levels withrespect to said frame means, and said pivotal mounting of said firstends of said towing bars at said spaced-apart points and said differentlevels being such that the towing bars are adapted to be crossed forsaid pivotal connection to the towing vehicle so that the trailer willtrack behind the towing vehicle.

7. A tracking trailer for freight containers as claimed in claim 6,comprising guide plate means pivotally mounted on the trailer bed formovement between an operative position above said bed and an inoperativeposition below said bed, said guide plate means comprising at least onepair of guide members disposed on opposite sides of the longitudinalaxis of the trailer bed, each said guide member being triangularlyshaped for at least a portion of its cross section, and each saidtriangularly-shaped portion forming sloped guide surfaces adapted to beengaged when in said operative position by said containers and to guidesaid containers to desired positions relative to said trailer bed.

8. A tracking trailer for freight containers as claimed in claim 6,wherein each said towing bar is hollow along substantially its entirelength.

9. A tracking trailer for freight containers as claimed in claim 8,wherein each said towing bar has a tensilecompression strength of atleast 100,000 pounds.

10. A tracking trailer for freight containers as claimed in claim 6,wherein each said towing bar comprises a central portion in the form ofa hollow steel tube.

11. A tracking trailer for freight containers as claimed in claim 10,wherein said tracking trailer is approximately 40 feet long, saidforward wheel means is rotatably connected to said tracking trailer at apoint approximately 11 feet from its forward end, each said towing baris connected to said frame means approximately 3 feet forward of therotatable connection of said forward wheel means to said bed, and eachsaid towing bar is approximately 12 feet long.

1. A dolly for supporting a semitrailer and connecting it to a towingvehicle for movement along substantially flat terrain, said dollycomprising chassis means including fifth wheel means for engaging asemitrailer, wheel means mounting said chassis means and including atleast one pair of wheels mounted on a common axis, a pair of towing barsof equal length each having a first end pivotally connected to one endof said chassis means and a second end having pivotal engaging means forpivotal connection to a towing vehicle, each said towing bar beingadapted to be manually connected to and discOnnected from a towingvehicle, said first ends of said towing bars being pivotally connectedto said one end of said chassis means at spaced-apart points on oppositesides of a line perpendicular to said common axis at a point midwaybetween said pair of wheels, said spaced-apart points being at differentvertical levels with respect to said chassis means, and said pivotalmounting of said first ends of said towing bars at said spaced-apartpoints and said different levels being such that the towing bars areadapted to be crossed for said pivotal connection to the towing vehicleso that the semitrailer will track behind the towing vehicle.
 2. A dollyas claimed in claim 1, wherein each said towing bar is hollow alongsubstantially its entire length.
 3. A dolly as claimed in claim 2,wherein each said towing bar has a tensile-compression strength of atleast 100,000 pounds.
 4. A dolly as claimed in claim 1, wherein eachsaid towing bar comprises a central portion in the form of a hollowsteel tube.
 5. A dolly as claimed in claim 4, wherein the semitrailer tobe connected to a towing vehicle is approximately 40 feet long, eachsaid towing bar is approximately 12 feet long, said semitrailercomprises kingpin means disposed approximately 11 feet from the forwardend of the semitrailer for engagement with said fifth wheel means ofsaid dolly, and said towing bars are connected to said dollyapproximately 3 feet forward of the expected center of engagement ofsaid kingpin means in said fifth wheel means.
 6. A tracking trailer forfreight containers for movement along substantially flat terrain,comprising an elongated flat bed for receiving freight containers, wheelmeans movably mounting and supporting said bed, said wheel meansincluding at least one pair of rear wheels mounted on a first commonaxis fixed relative to said bed and forward wheel means rotatablyconnected to said bed, said forward wheel means including frame meansand at least one pair of front wheels mounting said frame means, saidpair of front wheels being mounted on a second common axis, a pair oftowing bars of equal length each having a first end pivotally connectedto one end of said frame means and a second end having pivotal engagingmeans for pivotal connection to a towing vehicle, each said towing barbeing adapted to be manually connected to and disconnected from a towingvehicle, said first ends of said towing bars being pivotally connectedto said one end of said frame means at spaced-apart points on oppositesides of a line perpendicular to said second common axis at a pointmidway between said pair of front wheels, said spaced-apart points beingat different vertical levels with respect to said frame means, and saidpivotal mounting of said first ends of said towing bars at saidspaced-apart points and said different levels being such that the towingbars are adapted to be crossed for said pivotal connection to the towingvehicle so that the trailer will track behind the towing vehicle.
 7. Atracking trailer for freight containers as claimed in claim 6,comprising guide plate means pivotally mounted on the trailer bed formovement between an operative position above said bed and an inoperativeposition below said bed, said guide plate means comprising at least onepair of guide members disposed on opposite sides of the longitudinalaxis of the trailer bed, each said guide member being triangularlyshaped for at least a portion of its cross section, and each saidtriangularly-shaped portion forming sloped guide surfaces adapted to beengaged when in said operative position by said containers and to guidesaid containers to desired positions relative to said trailer bed.
 8. Atracking trailer for freight containers as claimed in claim 6, whereineach said towing bar is hollow along substantially its entire length. 9.A tracking trailer for freight containers as claimed in claim 8, whereineach said towing bar has a tensile-compression strength of at least100,000 pounds.
 10. A tracking trailer for freight containers as claimedin claim 6, wherein each said towing bar comprises a central portion inthe form of a hollow steel tube.
 11. A tracking trailer for freightcontainers as claimed in claim 10, wherein said tracking trailer isapproximately 40 feet long, said forward wheel means is rotatablyconnected to said tracking trailer at a point approximately 11 feet fromits forward end, each said towing bar is connected to said frame meansapproximately 3 feet forward of the rotatable connection of said forwardwheel means to said bed, and each said towing bar is approximately 12feet long.